Electrical power is distributed to components of an integrated circuit (IC) over a network of conductors, often referred to as a power grid. The power grid distributes power supply voltages from bond pad locations to the various transistors on the integrated circuit through metal traces formed in one or more layers. The metal traces used to route power supply voltages through an integrated circuit have resistance. Thus, there is typically a voltage drop across the power grid, typically referred to as an IR drop, due to the resistance of the metal traces of the power grid. The voltage seen at the component devices is therefore the power supply voltage less the IR drop and possibly additional loss factors.
Excessive voltage drops in the power grid may impair functionality of the integrated circuit. A number of techniques have been proposed or suggested for alleviating IR drop issues in power grids for integrated circuits. For example, bypass capacitance can be added to the power grid structure to reduce the IR drop. The traditional approach for adding bypass capacitance to a power grid is to place bypass capacitor cells in the standard cell rows. This approach, however, requires cell area and the bypass capacitors are comprised of transistors that have a high ESR (equivalent series resistance) and a leakage power associated with them. Thus, the added transistors increase the overall power consumption of the integrated circuit.
A need therefore remains for improved techniques for alleviating IR drop issues in integrated circuit power grids. A further need exists for techniques to alleviate IR drop issues in power grids where the bypass capacitance is built directly into the power grid, while saving on routing resources.